The present invention relates generally to a structure of a multi-domain liquid crystal display (MD-LCD), and more specifically to a structure of a multi-domain liquid crystal display with a wall-bump structure located around the central portion of a pixel.
The market for liquid crystal display (LCD) panels is increasing rapidly, especially in their applications to notebook PCs and monitors. When LCD panels of larger size and higher resolution are used for desktop monitors, navigation displays in cars, wall TVs and High-Definition TVs (HDTV), wide-viewing angles (WVA) and fast response time become very critical in meeting the monitors"" requirements. In addition to contrast ratio with respect to different viewing angles, gray-scale inversion, colorimetry, and the optical response of a LCD are important features of a high quality LCD panels. However, the cost associated with designing and manufacturing a panel also needs to be considered.
Controlling liquid crystal domains is the most important technology in obtaining a wide-viewing angle for a vertically aligned LCD. Most of the conventional LCDs are 90xc2x0 twisted nematic (TN) LCD""s having a LCD panel and crossed polarizers attached outside. The drawbacks of the conventional LCDs include narrow viewing angles (xc2x140xc2x0 horizontally and xc2x130xc2x0 vertically), slow response (about 50 ms), and large color dispersion. Therefore, it is difficult to make high quality LCD panels. Also, the rubbing process required in manufacturing the panels causes electric static damage (ESD) and particle pollution.
Because of the demand in high quality LCD panels with wide-viewing angles, the structure of multi-domain LCDs has been developed. Each pixel is divided into several domains to compensate for the asymmetry in optics so as to increase the viewing angle of the display panel. Such LCD panels have compensation films and crossed polarizers outside the liquid crystal display panel. The liquid crystal mode is multi-domain vertically aligned. A multi-domain LCD panel has a wide-viewing angle and small color dispersion. In addition, it does not have electric static damage and particle pollution problems because no rubbing process is required.
U.S. Pat. No. 5,309,264 discloses a structure of a multi-domain liquid crystal display. It uses a common electrode having a pattern of openings thereon to cause the liquid crystal molecules to be divided into multiple domains. Therefore, the display element comprises multi-domains. The characteristics of the domains are determined by the shape of the patterns on the electrodes. The shape of the patterns of openings in the electrodes may be xe2x80x9c+xe2x80x9d, xe2x80x9cXxe2x80x9d, xe2x80x9cdouble-Yxe2x80x9d, xe2x80x9ctriple-Xxe2x80x9d, xe2x80x9cdual double-Yxe2x80x9d, xe2x80x9cdiagonal slotxe2x80x9d, xe2x80x9chorizontal slotxe2x80x9d or xe2x80x9cvertical slotxe2x80x9d. FIG. 1(a) to FIG. 1(i) show some patterns of the openings in the electrodes. The pixels shown in FIG. 1(a) to FIG. 1(c) are of equal width and length while those shown in FIG. 1(d) to FIG. 1(i) typically have a 1:3 aspect ratio.
FIG. 2 shows a conventional bump structure of a multi-domain LCD. The W-shaped bump structures are formed on both upper and lower substrates. Although the rubbing process has been eliminated in manufacturing these LCD panels, complicated manufacturing steps are required. For example, it is necessary to form bump structures on both upper and lower substrates.
The primary object of the present invention is to provide a structure of a multi-domain liquid crystal display with wall-bump structures located at the central portion of a pixel and formed on a substrate of a color filter or thin film transistors (TFT).
According to the invention, the wall-bump structure provides pre-tilted angles for liquid crystal molecules and results in orderly alignment of the liquid crystal molecules to form multi-domain textures when an external voltage is applied. Also, the ratio of the light intensity in horizontal and vertical directions can be controlled by adjusting the position of the wall-bump structure.
In the preferred embodiments of a multi-domain liquid crystal display of the present invention, the wall-bump structure on an electrode may be formed by a combination of wall-bumps of different shapes. For a pixel with equal width and length, its wall-bump structure may be quasi-square or circular. Otherwise, it may be a combination of multiple quasi-square shaped wall-bumps and slot shaped wall-bumps, a combination of multiple circular shaped wall-bumps and slot shaped wall-bumps, a T-inverse- T shaped wall-bump, a combination of multiple T-inverse- T shaped wall-bumps and slot shaped wall-bumps, a V-inverse- V shaped wall-bump or a combination of multiple V shaped wall-bumps and inverse- V shaped wall-bumps.
In the present invention, standard photo-lithographic process is used to manufacture the wall-bump structure on common electrodes. The wall-bump structures is located at the central portion of each pixel. The electrodes on a substrate produce lateral fringe fields parallel to a substrate. This fringe field effect causes liquid crystal molecules to be tilted along a plane parallel to the substrate, and therefore establishes a multi-domain LCD cell. Furthermore, the ratios among the sizes of different domains can be adjusted by adjusting the position of the wall-bump structure. No rubbing treatment is needed in manufacturing the liquid crystal displays. The manufacturing process is greatly simplified and has the advantages of being fast, simple, clean and pollution free.